Semiconductor light emitting device and method for manufacturing the same

ABSTRACT

A semiconductor light emitting device having high reliability and excellent light distribution characteristics is provided. Specifically, a semiconductor light emitting device  1  is provided with an n-electrode  50 , which is arranged on a light extraction surface on the side opposite to the surface whereupon a semiconductor stack  40  is mounted on a substrate  10 . A plurality of convexes are arranged on a first convex region  80  and a second convex region  90  on the light extraction surface. The second convex region  90  adjoins to the interface between the n-electrode  50  and the semiconductor stack  40 , between the first convex region  80  and the n-electrode  50 . The base end of the first convex arranged in the first convex region  80  is positioned closer to alight emitting layer  42  than the interface between the n-electrode  50  and the semiconductor stack  40 , and the base end of the second convex arranged in the second convex region  90  is positioned closer to the interface between the n-electrode  50  and the semiconductor stack  40  than the base end of the first convex.

FIELD OF THE INVENTION

The present invention relates to a semiconductor light emitting device,and more particularly relates to a semiconductor light emitting devicewhich is provided with concaves/convexes on a light extraction surfacefor increasing light extraction efficiency, and a fabrication method forthe same.

DESCRIPTION OF THE RELATED ART

Conventionally, in the light emitting device such as LED, a plurality ofconcaves/convexes may be formed on a semiconductor layer surface of thelight extraction side for increasing light extraction efficiency fromthe semiconductor layer, and the electrode is also formed on a part ofthe semiconductor layer surface. Such technologies described in, forexample, JPn. Pat. Appln. KOKAI Publication No. 2000-196152, JPn. Pat.Appln. KOKAI Publication No. 2005-5679, JPn. Pat. Appln. KOKAIPublication No. 2003-69075, JPn. Pat. Appln. KOKAI Publication No.2005-244201 and JPn. Pat. Appln. KOKAI Publication No. 2006-147787 havebeen known.

In the light emitting device described in JPn. Pat. Appln. KOKAIPublication No. 2000-196152, many hemispherical concaves/convexes areformed spaced to each other on a semiconductor layer surface of thelight extraction side, a transparent electrode is formed on theconcaves/convexes and a bonding pad is selectively stacked on thetransparent electrode. A method for forming the concaves/convexes is asfollows. Namely, a plurality of aligned resists which are spaced apredetermined distance to each other are softened and melted by a heattreatment, then, the resists distorted into a hemispherical shape whichhas a semicircular shape in cross section is transferred to asemiconductor layer surface of the light extraction side to form theconcaves/convexes.

In the light emitting device described in JPn. Pat. Appln. KOKAIPublication No. 2005-5679, concaves/convexes having a two-dimensionalperiodic structure are formed on a semiconductor layer surface of thelight extraction side by etching. In the area that has noconcaves/convexes on the light extraction side, an n-electrode and ap-electrode are formed in respective different levels with a step.

The light emitting device described in JPn. Pat. Appln. KOKAIPublication No. 2003-69075 is fabricated by stacking a GaN-basedcompound semiconductor on a GaN-based compound semiconductor substrate,and concaves/convexes are formed, by etching, on a surface opposite to asurface on which a device fabricated on a GaN-based semiconductorsubstrate is stacked. Electrodes are formed on the concaves/convexes.

The light emitting device described in JPn. Pat. Appln. KOKAIPublication No. 2005-244201 includes a porous structure provided withmany long voids and an electrode surrounding the porous structure on asemiconductor layer surface of the light extraction side. A method forforming the porous structure is as follows. Namely, an n-typesemiconductor layer, an active layer, a p-type electron barrier layer, ap-type strained superlattice layer and a p-contact layer are formed inthis order on a sapphire wafer substrate. After an ohmic p-electrode isformed so as to form a periphery of a light extraction portion having anopening shape, the wafer that stacks each semiconductor layer is dippedin a chemical solution. Then, the porous structure is formed in thelight extraction portion of the p-contact layer. In this case, the ohmicp-electrode remains in the periphery portion surrounding the porousstructure. Meanwhile, after forming the porous structure, then-electrode is formed by etching.

The light emitting device described in JPn. Pat. Appln. KOKAIPublication No. 2006-147787 is provided with concaves/convexes which arenaturally formed originating from a threading dislocation produced in aninterface of the substrate when the crystal is grown, and an electrodeis formed on the concaves/convexes.

In addition, in a light emitting device provided with concaves/convexeson a surface of the light extraction side, a light emitting device thathas a p-electrode and an n-electrode on the side opposite to a surfaceof the light extraction side is described in JPn. Pat. Appln. KOKAIPublication No. 2007-88277. The light emitting device described in JPn.Pat. Appln. KOKAI Publication No. 2007-88277 is fabricated by stacking asemiconductor including a light emitting layer on a sapphire substrate,and includes convexes on a surface (surface on light extraction side)opposite to a surface on which the light emitting layer is formed on thesapphire substrate. The convexes are formed using a pattern, and consistof a mixture of a first convex which has a long periodic distance and isrelatively high and a second convex which has a short periodic distanceand is relatively low.

Meanwhile, a light emitting device that is supposed to haveconcaves/convexes on a surface of a nitride-based semiconductor layerjust under the electrode is described in JPn. Pat. Appln. KOKAIPublication No. 2007-67209. The light emitting device described in JPn.Pat. Appln. KOKAI Publication No. 2007-67209 is fabricated by stacking agallium nitride-based compound semiconductor on a gallium nitridesubstrate, and the concaves/convexes are formed on a surface opposite toa surface on which a device on the gallium nitride substrate is stacked.A method for forming the concaves/convexes is as follows. Namely, aftermacro concaves/convexes are formed by grinding, micro concaves/convexesare formed to be overlapped on the macro concaves/convexes by etching.This improves adhesiveness and contact resistance between the nitridesemiconductor and the electrode to be stacked thereon.

However, there were the following problems in the conventionaltechnologies.

The conventional technologies are technologies to disposeconcaves/convexes for increasing light extraction efficiency from asemiconductor layer. Therefore, in the case that improves a light outputas well as the light extraction efficiency, the following problems willbe caused.

For example, in the case that increases a light output by disposingconvexes on a semiconductor layer surface, the light output is likely tobe increased as the convexes become higher. In other words, the lightoutput is likely to be increased as the semiconductor surface is dug(shaved or etched) deeper.

On the other hand, in the light emitting devices described in JPn. Pat.Appln. KOKAI Publication No. 2000-196152, JPn. Pat. Appln. KOKAIPublication No. 2005-5679, JPn. Pat. Appln. KOKAI Publication No.2003-69075, JPn. Pat. Appln. KOKAI Publication No. 2005-244201 and JPn.Pat. Appln. KOKAI Publication No. 2006-147787, concaves/convexes areuniformly disposed on a semiconductor layer surface of the lightextraction side. Therefore, as the semiconductor layer surface is dugdeeper for increasing a light output, the electrode is more likely to bepeeled off. For example, in a light emitting device that separates anarea for the electrode from an area for the convex, it is required todispose deep concaves/convexes in the area close to the electrode in thecase that increases the light output as well as the light extractionefficiency, and thereby the electrode is likely to be peeled off.Therefore, in the case that increases the light output, while supposingto increase the light extraction efficiency, a highly reliable lightemitting device which can prevent the electrode formed on a surface ofthe light extraction side from peeling-off is expected.

In addition, a control of a light distribution of a light emittingdevice is important in designing the light emitting device. For example,the light emitting device described in JPn. Pat. Appln. KOKAIPublication No. 2000-196152 is poor in the light distribution becauseconcaves/convexes formed on a semiconductor layer surface are formed insemispherical. That is, a light extraction efficiency of a light emittedoutside from the concaves/convexes in the right upper direction becomespoor. Therefore, a technology not to degrade the light distribution whenthe light output is increased is expected.

The present invention has been developed in consideration of theforegoing problems, and it is an object of the present invention toprovide a semiconductor light emitting device which is highly reliableand excellent in light distribution.

It is another object of the present invention to provide a method forfabricating a semiconductor light emitting device which is highlyreliable and excellent in light distribution.

DISCLOSURE OF THE INVENTION

According to a first aspect of the present invention, there is provideda semiconductor light emitting device comprising a semiconductor stackincluding a light emitting layer between an n-type semiconductor layerand a p-type semiconductor layer, a substrate on which the semiconductorstack is mounted, an electrode disposed on a light extraction surfaceopposite to a surface that the semiconductor stack is mounted on thesubstrate, and a plurality of convexes on the light extraction surface,in which the plurality of the convexes are disposed in a first convexarea and a second convex area, the second convex area is located betweenthe first convex area and the electrode and is adjacent to an interfacebetween the electrode and the semiconductor stack, a base end of a firstconvex disposed in the first convex area is located to be closer to thelight emitting layer than the interface, and a base end of a secondconvex disposed in the second convex area is located to be closer to theinterface than the base end of the first convex.

In the configuration described above, the semiconductor light emittingdevice is provided with the first convex area and the second convex areain the light extraction surface, and the second convex area is disposedadjacent to the electrode. Therefore, a peeling-off of the electrode ofthe light emitting device can be reduced in comparison with that of alight emitting device which is uniformly provided with only the firstconvex which is formed from a relatively deep level on the lightextraction surface, while homogenizing a current dispersion in thesemiconductor layer. In addition, a light distribution of thesemiconductor light emitting device can be improved in comparison withthat of a semiconductor light emitting device which is uniformlyprovided with only the first convex which is formed from a relativelydeep level in the light extraction surface, as well as provided with noconcaves/convexes in an area adjacent to the electrode. Furthermore, alight output of the semiconductor light emitting device can be increasedin comparison with that of a semiconductor light emitting device whichis uniformly provided with only the second convex which is formed from arelatively shallow level in the light extraction surface.

In addition, in the semiconductor light emitting device according to thepresent invention, it is preferable that a height from the base end to atop end of the first convex is larger than a height from the base end toa top end of the second convex. In the configuration, the lightextraction surface is provided with the first convex area where theconvex is formed to be high from a relatively deep level and the secondconvex area where the convex is formed to be low from a relativelyshallow level, and the second convex area is arranged adjacent to theelectrode. Therefore, due to the configuration described above, thepeeling-off of the electrode can be reduced and the light distributionof the semiconductor light emitting device can be improved. Here, it ispreferable that a height of the first convex is more than twice of thatof the second convex.

In addition, in the semiconductor light emitting device according to thepresent invention, it is preferable that the top end of the first convexand the top end of the second convex are tapered off to a point. In theconfiguration, a light extraction efficiency in the right abovedirection of a light emitted outside from the first convex and thesecond convex is improved. Then, the light distribution can be improvedin comparison with the case that the top end is not tapered off to apoint.

In addition, the semiconductor light emitting device according to thepresent invention may be configured in such a manner that at least thesecond convex area is disposed so as to surround the electrode. In theconfiguration, the light distribution is improved in comparison with thecase that the second convex area is adjacent to only a part of theelectrode. In addition, a degree of freedom in designing an electrodeshape and an arrangement position thereof in the light extractionsurface can be increased. Here, it is sufficient as long as the secondconvex area surrounds at least the electrode, and, for example, thesecond convex area may be disposed at an outer periphery of the firstconvex area, while surrounding the electrode.

In addition, in the semiconductor light emitting device according to thepresent invention, it is preferable that the first convex area isdisposed so as to surround the second convex area and the electrode. Inthe configuration, the first convex area is arranged apart from theelectrode and in high density, thereby resulting in high light output.

In addition, the semiconductor light emitting device according to thepresent invention may be configured in such a manner that the electrodesare disposed on the light extraction surface apart from each other, andthe first convex area and the second convex area are disposed in an areabetween the electrodes. In the configuration, when a plurality ofelectrodes are disposed on the light extraction surface apart from eachother at a predetermined distance, each electrode can be prevented frompeeling-off, and the light distribution can be improved.

In addition, in the semiconductor light emitting device according to thepresent invention, it is preferable that the top end of the first convexand the top end of the second convex are formed in a non-flat shape. Inthe configuration, the light distribution can be improved in comparisonwith the case that the top end is a flat shape. Here, the non-flat topend includes a top end having a curved surface, a pointed top end, and atop end having concaves/convexes at the top.

In addition, in the semiconductor light emitting device according to thepresent invention, it is preferable that a base end of the first convexis disposed adjacent to a base end of an adjacent first convex, and abase end of the second convex is disposed adjacent to a base end of anadjacent second convex. In the configuration, the light extractionefficiency in the right above direction of a light emitted outside fromthe convexes can be increased in comparison with the case that hasspaces of flat surfaces among base ends of adjacent convexes. Then, thelight distribution is improved. In addition, neighboring of base ends ofadjacent convexes corresponds to the status that a surface which hasspaces among base ends of adjacent convexes is further deeply etched,thereby resulting in increase in the light output.

In addition, the semiconductor light emitting device according to thepresent invention may be configured in such a manner that the base endof the first convex in the first convex area is formed to be closer tothe light emitting layer as the first convex leaves the electrode. Inthe configuration, the convex is deepened with two steps in the lightextraction surface. The convex in the first convex area is formed to bedeeper than that of the second convex area which is disposed closer tothe electrode than the first convex area, and even in the first convexarea, the convex is formed to become gradually or continuously deeper asthe convex leaves the electrode. As a result, the light output can beincreased, while reducing the peeling-off of the electrode.

In addition, the semiconductor light emitting device according to thepresent invention may be configured in such a manner that a third convexis further disposed in the interface between the electrode and thesemiconductor stack. In the configuration, in addition to that the lightoutput can be increased, a contact resistance between the third convexand the electrode which is stacked on the third convex after the thirdconvex is formed on the surface of the light extraction side of thesemiconductor stack, and the adhesiveness between the surface of thelight extraction side and the electrode can be improved. Here, the thirdconvex may have a shape and a size identical to those of the firstconvex or the second convex, and further, may have a shape and a sizedifferent from those of the first convex and the second convex.

According to a second aspect of the present invention, there is provideda method for fabricating a semiconductor light emitting devicecomprising steps for forming a semiconductor stack including a lightemitting layer between an n-type semiconductor layer and a p-typesemiconductor layer, for forming a resist having an opening surroundingan electrode formation planned area on a semiconductor layer surfacewhich forms a light extraction surface opposite to a surface that thesemiconductor stack is mounted on a substrate in such a manner that theopening is narrowed toward a stacking direction of the resist, forstacking a mask material on the semiconductor layer surface through theresist, for removing the resist on which the mask material is stacked,and for etching the semiconductor layer surface by masking the electrodeformation planned area.

According to the procedure described above, the method for fabricating asemiconductor light emitting device includes a step for forming theresist having the opening which is narrowed toward the stackingdirection of the resist. Therefore, if a mask material is stacked on thesemiconductor layer surface through the resist formed as describedabove, the mask material injected through the opening is slightly spreadon the side of the resist on the semiconductor layer surface, and formsa guard-shaped area which is wider than the opening. Then, when theresist on which the mask material is stacked is removed, the maskmaterial having a cross section identical to a shape of the opening ofthe resist remains in the electrode formation planned area on thesemiconductor layer surface. In addition, a thin guard-shaped area madeof the mask material is formed so as to surround the electrode formationplanned area. Next, when the semiconductor layer surface is etched bymasking the electrode formation planned area, the convex is formed earlyin the area that has no mask material. In this case, in the guard-shapedarea, the thin mask material is gradually removed and the semiconductoris exposed, and finally, the convex is formed late. Through theprocesses described above, two types of convexes having differentheights can be formed. Then, it is unnecessary to etch twice for formingthe two types of convexes, and the fabrication process can be shortened,accordingly.

In addition, in the method for fabricating a semiconductor lightemitting device according to the present invention, it is preferable tofurther comprise a step for using an electrode material as the maskmaterial. In the procedure, the method for fabricating a semiconductorlight emitting device includes the step for removing the resist on whichthe electrode material as a mask material is stacked. Therefore, theelectrode having across section identical to a shape of the opening ofthe resist can be formed by the step in the electrode formation plannedarea on the semiconductor layer surface, and accordingly, thefabrication process can be shortened.

According to the semiconductor light emitting device of the presentinvention, a peeling-off of the electrode on the side of the lightextraction surface can be reduced, and a current dispersion in thesemiconductor layer can be homogenized, while increasing the lightextraction efficiency. Then, a semiconductor light emitting device whichis highly reliable and excellent in light output can be provided. Inaddition, the light output has a maximum value at directivity angle 0°,and the light distribution is close to the Lambert's law. Therefore, asemiconductor light emitting device suitable for, for example, lightingcan be provided. In addition, according to the present invention, asemiconductor light emitting device which is highly reliable andexcellent in light distribution can be fabricated, while shortening thefabrication process. Here, the excellent light distribution in thepresent invention means that the light output has the maximum value atdirectivity angle 0°, and the light distribution is close to theLambert's law. As a result, a light emitting device which is excellentand easy in designing of, for example, lighting or an automobileheadlamp can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view schematically showing a structure of asemiconductor light emitting device according to an embodiment of thepresent invention;

FIG. 2 is a plan view showing an example of an n-electrode shown in FIG.1;

FIG. 3 is a perspective view schematically showing a first convex areaand a second convex area shown in FIG. 1;

FIG. 4 is a cross sectional view taken along A-A line shown in FIG. 3;

FIG. 5A to FIG. 5E are cross sectional views schematically showing afabrication process of the semiconductor light emitting device shown inFIG. 1 (Part 1);

FIG. 6A to FIG. 6F are cross sectional views schematically showing thefabrication process of the semiconductor light emitting device shown inFIG. 1 (Part 2);

FIG. 7 is a cross sectional view schematically showing the fabricationprocess of the semiconductor light emitting device shown in FIG. 1 (Part3);

FIG. 8 is a graph showing an example of a light directionality of asemiconductor light emitting device according to the embodiment of thepresent invention;

FIG. 9 is a partial cross sectional view schematically showing the firstconvex area as a modified example of a semiconductor light emittingdevice according to the embodiment of the present invention;

FIG. 10 is a cross sectional view schematically showing a modifiedexample of a structure of a semiconductor light emitting deviceaccording to the embodiment of the present invention;

FIG. 11 is a cross sectional view schematically showing a modifiedexample of a structure of a semiconductor light emitting deviceaccording to the embodiment of the present invention;

FIG. 12 is a cross sectional view schematically showing a structure of aconventional semiconductor light emitting device; and

FIG. 13 is a cross sectional view schematically showing a structure of aconventional semiconductor light emitting device.

BEST MODE FOR EMBODYING THE INVENTION

Hereinafter, a best mode (hereinafter, referred to as embodiment) forembodying a semiconductor light emitting device according to the presentinvention will be explained by referring to drawings. It is noted thatthicknesses and lengths of, for example, constituents shown in thedrawings are enlarged for the purpose of clearly explaining thearrangements, then, the thicknesses and lengths are not limited to thoseshown in the drawings.

[Structure of Light Emitting Device]

A light emitting device according to an embodiment of the presentinvention relates to a light emitting device which is provided with aplurality of convexes and an electrode on a light extraction surface ofa semiconductor stack, which has a light emitting layer between ann-type semiconductor layer and a p-type semiconductor layer, opposite tothe surface to be mounted on a substrate. First, a structure of thesemiconductor light emitting device will be explained by referring toFIG. 1 to FIG. 4. FIG. 1 is a cross sectional view schematically showinga structure of a semiconductor light emitting device according to theembodiment of the present invention, and FIG. 2 is a plan view showingan example of an n-electrode shown in FIG. 1. In addition, FIG. 3 is aperspective view schematically showing a first convex area and a secondconvex area shown in FIG. 1, and FIG. 4 is a cross sectional view takenalong A-A line shown in FIG. 3.

As shown in FIG. 1, a semiconductor light emitting device 1 according tothe embodiment mainly consists of a substrate 10, a metallization layer20, a p-electrode 30, a semiconductor stack 40, an n-electrode 50, apassivation film 60 and a backside metallization layer 70.

(Substrate)

The Substrate 10 is Made of Silicon (Si). Meanwhile, other than Si, forexample, a semiconductor substrate made of a semiconductor such as Ge,SiC, GaN, GaAs, GaP, InP, ZnSe, ZnS and ZnO, or a single metalsubstrate, or a metal substrate made of a complex of metals whichconsists of not less than two metals which are mutually immiscible orhave a small solid solubility limit to each other may be used. As thesingle metal substrate, specifically, a Cu substrate can be used. Inaddition, as the metal substrate, specifically, a substrate consistingof at least one metal selected from a highly-conductive metal such asAg, Cu, Au and Pt and at least one metal selected from a high hardnessmetal such as W, Mo, Cr and Ni may be used. When the substrate 10 whichis made of a semiconductor material is used, a device, for example, azener diode may be added to the substrate 10. Further, as the metalsubstrate, a complex of Cu—W or Cu—Mo may be preferably used.

(Metallization Layer)

A metallization layer 20 is a eutectic alloy for bonding two substratesin the fabrication process of the semiconductor light emitting device 1.Specifically, a metallization layer 21 on the epitaxial (growth) sideshown in FIG. 5C and a metallization layer 22 on the substrate sideshown in FIG. 5D are bonded to form the metallization layer 20. Themetallization layer 21 on the epitaxial side may be formed by stacking,for example, Ti/Pt/Au/Sn/Au in this order from the bottom in FIG. 5C. Inaddition, the metallization layer 22 on the substrate side may be formedby stacking, for example, Au/Pt/TiSi₂, or TiSi₂/Pt/Pd in this order fromthe top in FIG. 5D.

Returning to FIG. 1, the explanation for the structure of thesemiconductor light emitting device 1 will be continued.

(p-Electrode)

A p-electrode 30 is formed on a mounting surface of a semiconductorstack 40 on the side of the substrate 10.

Specifically, the p-electrode 30 consists of at least two layers, thatis, a p-electrode first layer (not shown) on the side of thesemiconductor stack 40 and a p-electrode second layer (not shown) on thebottom side of the p-electrode first layer.

The following materials are commonly used for the p-electrode firstlayer (not shown). For example, a metal such as Ag, Zn, Ni, Pt, Pd, Rh,Ru, Os, Ir, Ti, Zr, Hf, V, Nb, Ta, Co, Fe, Mn, Mo, Cr, W, La, Cu and Y,and an alloy thereof, and a single film or a stacked film of, forexample, conductive oxides such as ITO, ZnO and SnO₂ may be used. Withrespect to the p-electrode second layer (not shown), for example, Pt, Auand Ni—Ti—Au based electrode material may be used.

Specifically not shown, but if the p-electrode 30 consists of atwo-layer structure of the p-electrode first layer/the p-electrodesecond layer, a stacked layer structure of, for example, Pt/Au, Pd/Au,Rh/Au and Ni/Au may be used. In addition, if the p-electrode 30 consistsof a three-layer structure including a p-electrode third layer betweenthe p-electrode first layer and the p-electrode second layer, a stackedlayer structure of, for example, Ni/Pt/Au, Pd/Pt/Au and Rh/Pt/Au may beused. Furthermore, if the p-electrode 30 consists of a four-layerstructure including the p-electrode third layer and a p-electrode fourthlayer between the p-electrode first layer and the p-electrode secondlayer, a stacked layer structure of, for example, Ag/Ni/Ti/Pt may beused.

(Semiconductor Stack)

The semiconductor stack 40 is made of, for example, GaN-based compoundsemiconductor which is generally expressed by In_(x)Al_(y)Ga_(1-x-y)N(0≦x≦1, 0≦y≦1, 0≦x+y≦1). Specifically, the GaN-based compoundsemiconductor is, for example, GaN, AlGaN, InGaN and AlGaInN.Especially, GaN is preferable because an etched surface of GaN has anexcellent crystalline surface. The semiconductor stack 40 is formed bysequentially stacking an n-type semiconductor layer 41, a light emittinglayer 42 and a p-type semiconductor layer 43 in this order from the sideof the light extraction surface opposite to a surface of thesemiconductor stack 40 to be mounted on the substrate 10.

A plurality of convexes are formed on the light extraction surface. Inthe embodiment, the light extraction surface is a surface of the n-typesemiconductor layer 41. That is, the plurality of convexes are disposedon the n-type semiconductor layer 41. The plurality of convexes aredisposed in a first convex area 80 and a second convex area 90 (90 a, 90b, 90 c, 90 d). The second convex area 90 is located between the firstconvex area 80 and the n-electrode 50, and neighbored an interfacebetween the n-electrode 50 and the semiconductor stack 40. A base end ofthe first convex formed in the first convex area 80 is located at aposition closer to the light emitting layer 42 than the interfacebetween the n-electrode 50 and the semiconductor stack 40. Abase end ofthe second convex formed in the second convex area 90 is located at aposition closer to the interface between the n-electrode 50 and thesemiconductor stack 40 than the base end of the first convex. A heightof the first convex from the base end to the top end is larger than thatof the second convex. Two n-electrodes 50 are disposed on the lightextraction surface spaced to each other, and the first convex area 80and the second convex areas 90 a, 90 b exist in an area between the twon-electrodes 50 which are disposed spaced to each other. The convexes(first convex, second convex) formed in the first convex area 80 and thesecond convex area 90 will be explained later in detail.

The n-type semiconductor layer 41 is made of GaN containing, forexample, Si, Ge or O (oxygen) as an n-type impurity. The n-typesemiconductor layer 41 may be formed by a plurality of layers.

The light emitting layer 42 is made of, for example, InGaN.

The p-type semiconductor layer 43 is made of GaN containing, forexample, Mg as a p-type impurity.

Two electrodes are formed on the light extraction surface of thesemiconductor stack 40. In the embodiment, since the light extractionsurface is a surface of the n-type semiconductor layer 41, an electrodeformed on the light extraction surface is the n-electrode 50. Meanwhile,a number of the electrode to be formed on the light extraction surfacemay be one or more.

(n-Electrode)

As shown in FIG. 1, the n-electrodes 50 are disposed on the lightextraction surface at a predetermined distance. In the embodiment, sincethe light extraction surface is a surface of the n-type semiconductorlayer 41, the n-electrodes 50 are formed on an upper surface of then-type semiconductor layer 41 at a predetermined distance andelectrically connected. The n-electrode 50 is connected to the outsideby a bonding wire. The n-electrode 50 consists of a multilayer filmincluding a plurality of metals, for example, Ti/Pt/Au, Ti/Pt/Au/Ni,Ti/Al, Ti/Al/Pt/Au, W/Pt/Au, V/Pt/Au, Ti/TiN/Pt/Au and Ti/TiN/Pt/Au/Niin this order from the upper side of the n-type semiconductor layer 41.The metals are stacked in these orders from the upper side of the n-typesemiconductor layer 41. Meanwhile, the n-electrode 50 may be consistingof an ohmic electrode and a pad electrode.

In an example shown in FIG. 2, two n-electrodes 50 having approximatelya line shape are disposed parallel in the semiconductor light emittingdevice 1 at a predetermined distance, and wires 51, 52 are connected tothe respective n-electrodes 50. The second convex area 90 is disposedsurrounding the n-electrode 50. For example, the n-electrode 50 to whichthe wire 51 is connected corresponds to the electrode surrounded by thesecond convex areas 90 a, 90 c shown in FIG. 1. Similarly, then-electrode 50 to which the wire 52 is connected corresponds to theelectrode surrounded by the second convex areas 90 b, 90 d shown inFIG. 1. Here, as shown in FIG. 2, the second convex areas 90 a, 90 cshown in FIG. 1 are the areas that are given two numerical numbers tothe unique second convex area 90 for convenience. This is the same withthe second convex areas 90 b, 90 d shown in FIG. 1. In addition, thefirst convex area 80 is disposed surrounding the second convex area 90and the n-electrode 50. Namely, the first convex area 80 surrounds onen-electrode 50 to which the wire 51 is connected and the second convexarea 90 surrounding the one n-electrode 50, and the other n-electrode 50to which the wire 52 is connected and the second convex area 90surrounding the other n-electrode 50.

Returning to FIG. 1, the explanation for the structure of thesemiconductor light emitting device 1 will be continued.

(Passivation Film)

A passivation film 60 is made of a transparent material which has arefractive index lower than that of the n-type semiconductor layer 41,and covers a surface of an upper surface of the n-electrode 50 exceptthe wire bonding area and a surface as well as a side face of the n-typesemiconductor layer 41. The passivation film 60 is made of an insulatorfilm, and preferably made of an oxide film. The passivation film 60 ismade of, for example, SiO₂ or ZrO₂.

The passivation film 60 may be formed by a well known method, such assputtering, ECR (Electron Cyclotron Resonance) sputtering, CVD (ChemicalVapor Deposition), ECR-CVD, ECR-plasma CVD, evaporation and EB (ElectronBeam). The passivation film 60 is preferably formed by, for example, ECRsputtering, ECR-CVD and ECR-plasma CVD.

(Backside Metallization Layer)

A backside metallization layer 70 is formed on a surface of thesubstrate 10 opposite to a surface on which a metallization layer 20 isformed, and functions as an ohmic electrode. As the backsidemetallization layer 70, for example, a metal stack of TiSi₂/Pt/Au, whichare sequentially stacked in this order from the upper side in FIG. 1,may be used.

(First Convex Area and Second Convex Area)

As shown in FIG. 3 and FIG. 4, the first convex formed in the firstconvex area 80 and the second convex formed in the second convex area 90b (90) have a top end that tapers off toward the top end, and a lightdistribution of the semiconductor light emitting device becomes good bythis taper. In addition, the top end of the first convex and the secondconvex is formed in a curved surface. Therefore, the light distributionis good in comparison with a case where the top end is formed in flat.As shown in FIG. 3 and FIG. 4, a height of the first convex is more thantwice of that of the second convex. In addition, a base end of each ofthe first convex and the second convex is disposed so as to neighbor abase end of the adjacent convex to each other. That is, there is no flatsurface between the adjacent convexes (first convex, second convex) toeach other. Since the convex is formed in such a high density, the lightextraction efficiency can be increased, thereby resulting in good lightdistribution. Furthermore, if a depth of the convex is the same, theforgoing case that has no flat surface between the convexes has a highlight output in comparison with a case having a flat surface between theconvexes.

[Fabrication Method of Semiconductor Light Emitting Device] (FirstFabrication Method)

A first fabrication method of a semiconductor light emitting deviceshown in FIG. 1 will be explained by referring to FIG. 5 and FIG. 6 (seeFIG. 1 to FIG. 4 as appropriate). FIG. 5 and FIG. 6 are cross sectionalviews schematically showing the fabrication method of the semiconductorlight emitting device shown in FIG. 1.

First, as shown in FIG. 5A, the n-type semiconductor layer 41, the lightemitting layer 42 and the p-type semiconductor layer 43 are stacked inthis order on a semiconductor growing substrate 100 to form thesemiconductor stack 40. The semiconductor growing substrate 100 is asubstrate to be removed in a later process, and made of, for example,sapphire having any one of a C-plane, R-plane and A-plane as a principalplane. Meanwhile, a substrate different from the sapphire substrate maybe used for the semiconductor growing substrate 100. As a substratedifferent from the sapphire substrate, for example, an insulatorsubstrate such as spinel (MgAl₂O₄), SiC (including 6H, 4H and 3C), ZnS,ZnO, GaAs and an oxide substrate whose lattice matches with the latticesof nitride semiconductors, which are well known and on which nitridesemiconductors can be grown, may be used.

Next, as shown in FIG. 5B, a p-electrode first layer and a p-electrodesecond layer, which are not shown, are stacked in this order on an uppersurface of the semiconductor stack (surface of p-type semiconductorlayer 43) to form a p-electrode 30 using magnetron sputtering. Next, asshown in FIG. 5C, a metallization layer 21 on the epitaxial layer sideis stacked on the p-electrode 30. In addition, before or after, or inparallel with forming the metallization layer 21, as shown in FIG. 5D, ametallization layer 22 is stacked on the substrate 10. Next, as shown inFIG. 5E, the substrate 10 on which the metallization layer 22 is stackedis turned over, and the metallization layer 22 on the substrate side andthe metallization layer 21 on the epitaxial side are bonded to eachother.

Next, as shown in FIG. 6A, the semiconductor growing substrate 100 isremoved from the semiconductor stack 40. As shown in FIG. 6B, an uppersurface (surface of n-type semiconductor layer 41) of the semiconductorstack 40, which is an uppermost surface due to turning over of thesubstrate 10 from which the semiconductor growing substrate 100 isremoved, is polished by CMP (Chemical Mechanical Polishing).

The upper surface (surface of n-type semiconductor layer 41) that is theuppermost surface of the semiconductor stack 40 is a surface of thelight extraction surface. Dry-etching and wet-etching both may be usedfor forming the first convex area 80 and the second convex area 90 onthe light extraction surface. However, wet-etching is preferable inorder to obtain a top end of the convex having a curved surface and toobtain a structure where base ends of the convexes are arranged closetogether. Then, a method for forming the convex using wet-etching willbe described next. Here, as a solution of wet-etching, a KOH aqueoussolution, TMAH (Tetramethyl ammonium hydroxide) and EDP (Ethylenediamine pyrocatechol) may be used as an anisotropic etching solution.

Next, as shown in FIG. 6C, n-electrodes 50 are formed on the uppersurface (surface of n-type semiconductor layer 41) of the semiconductorstack 40 at a predetermined distance. Next, as shown in FIG. 6D, a mask110 which entirely covers an upper surface and a side face of then-electrodes 50 is disposed, and a non-masked area is etched bywet-etching. The non-masked area is an area to be the first convex area80, and many imperfect first convexes are formed by the etching. Namely,a low convex projecting from a relatively shallow level is formed.Meanwhile, a working amount (depth) and a height of the convex can beadjusted by changing a temperature and a dipping time of thewet-etching. For example, a temperature of the etching solution may beraised to 50 to 100° C., and the dipping time may be set to, forexample, 30 minutes.

Next, the mask 110 is removed, and as shown in FIG. 6E, a non-maskedarea is wet-etched using the n-electrode 50 as a mask. In an area wherethe imperfect first convexes were formed within the non-masked area,many first convexes are formed by this etching. Namely, a high convexprojecting from a relatively deep level is formed. In addition, in anarea where the mask 110 was formed, many second convexes are formed bythis etching. Namely, a low convex projecting from a relatively shallowlevel is formed.

Next, as shown in FIG. 6F, the upper surface (surface of n-typesemiconductor layer 41) of the semiconductor stack 40 is covered with apassivation film 60. Meanwhile, the upper surface of the n-electrode 50except an area for wire bonding and a side face of the semiconductorstack 40 are covered with the passivation film 60. Then, a backsidemetallization layer 70 is formed as an ohmic electrode on a surface ofthe substrate 10 which is the uppermost surface due to turning over ofthe substrate 10, and the wafer on which the light emitting devices areformed is cut into chips. After that, the chip is mounted via thebackside metallization layer 70, and a wire is bonded to the n-electrode50 to fabricate the semiconductor light emitting device 1 shown in FIG.1.

(Second Fabrication Method)

Each of the processes shown in FIG. 5A to FIG. 5E and FIG. 6A to FIG. 6Bis conducted in a second fabrication method of the light emitting deviceshown in FIG. 1 as with the first fabrication method. The secondfabrication method is characterized by a method for forming then-electrode 50 following the process shown in FIG. 6C. The secondfabrication method will be explained by referring to FIG. 7 (see FIG. 1to FIG. 6F as appropriate). FIG. 7 is a cross sectional viewschematically showing a fabrication process of the light emittingdevice. It is noted that the layers below the semiconductor stack 40 areomitted in the illustration.

As shown in FIG. 7, a resist 120 is disposed on an electrode formationnon-planned area of the upper surface (surface of n-type semiconductorlayer 41) of the semiconductor stack 40. Here, the resist 120 which hasan opening surrounding an electrode formation planned area on the uppersurface of the semiconductor stack 40 is formed so as to narrow theopening toward a stacking direction (toward surface) of the resist 120.Next, the upper surface of the semiconductor stack 40 is entirelycovered with an electrode material 130 through the resist 120.Therefore, the electrode material 130 which is injected from the openingis slightly spread toward the resist 120 on the upper surface of thesemiconductor stack 40, and a guard-shaped area which is wider than theopening is formed. Subsequently, when the resist 120 on which theelectrode material 130 is disposed is removed, the n-electrode 50 isformed on the electrode formation planned area. In this case, aguard-shaped portion 50 a is formed so as to surround the n-electrode50.

After that, a non-masked area of the semiconductor stack 40 is etched bywet-etching using the n-electrode 50 (electrode formation planned area)as a mask. Here, a convex is formed earlier in an area where theguard-shaped portion 50 a is not formed. In this case, in the area ofthe guard-shaped portion 50 a, the thin electrode is gradually removed,and the upper surface of the semiconductor stack 40 is graduallyexposed, and finally, a convex is formed later. As a result, two typesof convexes (first convex, second convex) which have different heightsto each other can be formed. That is, the area where the guard-shapedportion 50 a is not formed becomes the first convex area 80, and thearea of the guard-shaped portion 50 a becomes the second convex area 90.As a result, since it is unnecessary to etch twice for forming the firstconvex area 80 and the second convex area 90, the fabrication processcan be shortened. Meanwhile, since the processes after the etching arethe same with those of the first fabrication method, the explanationwill be omitted.

[Characteristics of Semiconductor Light Emitting Device]

With respect to the characteristics of the semiconductor light emittingdevice 1 according to the embodiment, a light output, an electrodepeeling-off rate and a light distribution will be explained.

(Light Output)

The semiconductor light emitting device 1 according to the embodiment isprovided with the first convex area 80 having the first convex which isformed from a relatively deep level and relatively high, and the secondconvex area 90 having the second convex which is formed from arelatively shallow level and relatively low on the light extractionsurface. Therefore, the light output of the light emitting device can beincreased in comparison with a light emitting device which is providedwith only the second convex in a whole area on the light extractionsurface. In addition, as will be described later, since the electrodepeeling-off rate is low and the light distribution is excellent, thefirst convex can be formed to be high, and thereby the light output canbe increased.

(Electrode Peeling-Off Rate and Light Output)

For comparison, an example (hereinafter, referred to as COMPARATIVEEXAMPLE 1) was fabricated, where the second convex was formed from arelatively deep level as with the first convex and concaves/convexeswere formed by dry-etching using RIE (Reactive Ion Etching). As shown inFIG. 12, a conventional semiconductor light emitting device 200 thatshows the COMPARATIVE EXAMPLE 1 mainly consists of a substrate 210, ametallization layer 220, a p-electrode 230, a semiconductor stack 240,an n-electrode 250, a passivation film 260 and a backside metallizationlayer 270. The semiconductor stack 240 is formed by stacking an n-typesemiconductor layer 241, a light emitting layer 242 and a p-typesemiconductor layer 243 in this order from a side of the lightextraction surface which is an opposite surface of the semiconductorstack 240 to be mounted on the substrate 210. In addition,concaves/convexes 280 are regularly formed in an electrode formationnon-planned area on the surface of the n-type semiconductor layer 241.The n-electrode 250 is formed on the area other than theconcaves/convexes 280 on the light extraction surface that is a surfaceof the n-type semiconductor layer 241. It is noted that in FIG. 12,examples of the concaves/convexes 280 are schematically shown, and thesemiconductor light emitting device 200 includes at least a flat surface(upper surface) among the adjacent concaves to each other, or a flatsurface (bottom surface) among the adjacent convexes to each other inthe concaves/convexes 280.

In the semiconductor light emitting device 200, adhesion strengthbetween the n-electrode 250 and the n-type semiconductor layer 241 islowered in comparison with that of the semiconductor light emittingdevice 1 according to the embodiment of the present invention. This wassupposed to be caused by damages on the electrode joint portion by theconcaves/convexes 280. Then, in order to remove the damages, asemiconductor light emitting device having a flat surface withoutdisposing the concaves/convexes 280 was fabricated (hereinafter,referred to as COMPARATIVE EXAMPLE 2). As shown in FIG. 13, aconventional semiconductor light emitting device 300 that shows theCOMPARATIVE EXAMPLE 2 has the same structure with the semiconductorlight emitting device 200 shown in FIG. 12 except that a flat surface310 is formed between the n-electrodes 250 on the light extractionsurface that is a surface of the n-type semiconductor layer 241. It wasfound that adhesion strength of the electrode of the semiconductor lightemitting device 300 was improved. Specifically, in the semiconductorlight emitting device 200 (COMPARATIVE EXAMPLE 1) shown in FIG. 12, apeeling-off of the n-electrode 250 occurred at a rate of 6% when a wireis bonded on the n-electrode 250. But, in the semiconductor lightemitting device 300 (COMPARATIVE EXAMPLE 2) shown in FIG. 13, thepeeling-off of the electrode 250 was not observed. However, since thesemiconductor light emitting device 300 (COMPARATIVE EXAMPLE 2) shown inFIG. 13 has the flat surface 310, a total light output was decreased.

(Light Distribution)

FIG. 8 is a graph showing an example of a light directionality of asemiconductor light emitting device according to the embodiment of thepresent invention. Here, a light output of a semiconductor lightemitting device (hereinafter, referred to as EXAMPLE 1) whose firstconvex area 80 and second convex area 90 were etched using a KOHsolution as an etchant for wet-etching is shown with a thick solid line.In addition, a light output of a semiconductor light emitting device(hereinafter, referred to as EXAMPLE 2) where at least a height of thefirst convex was formed to be lower than that of the EXAMPLE 1 byadjusting a working amount (depth) is shown with a thin line.Furthermore, a light output of the forgoing COMPARATIVE EXAMPLE 1 isshown with a dashed line, and a light output of the forgoing COMPARATIVEEXAMPLE 2 is shown with a dashed-dotted line.

In FIG. 8, the horizontal axis indicates a radiation angle) (°), and thevertical axis indicates a light output (μW). Here, a directivity angle−90˜90° indicates an angle measured in a width direction (lateraldirection) of the n-electrode 50 shown in FIG. 2. In the directivityangle defined in the present invention, a direction vertical to thelight extraction surface is set to 0 (zero) degree, and a lightintensity at each angle of the light extraction direction was measured.For example, in FIG. 2, a direction vertical to the paper surface isdirectivity angle 0 (zero) degree. As shown in FIG. 8, the EXAMPLE 1 andthe EXAMPLE 2 have the largest light output at least at directivityangle 0°. This shows a light distribution according to the Lambert'slaw, or a light distribution close to the Lambert's law. On the otherhand, the COMPARATIVE EXAMPLE 1 has a larger light output at directivityangle ±30° than that of at directivity angle 0°. That is, thesemiconductor light emitting device 1 according to the embodiment of thepresent invention has the light distribution better than that of theconventional semiconductor light emitting device. In addition, a lightoutput of the COMPARATIVE EXAMPLE 2 was decreased totally at anydirectivity angle. Here, a light output in the light extractiondirection corresponds to an area surrounded by each curved line in thegraph. Specifically, assuming that a light output of the COMPARATIVEEXAMPLE 2 is “1”, a light output of the COMPARATIVE EXAMPLE 1 was“2.57”, a light output of the EXAMPLE 1 was “2.70”, and a light outputof the EXAMPLE 2 was “2.64”. Furthermore, with respect to a lightintensity at directivity angle 0°, assuming that a light intensity ofthe COMPARATIVE EXAMPLE 2 is “1”, a light intensity of the COMPARATIVEEXAMPLE 1 was “about 3 (about 3 times)” and light intensities of theEXAMPLE 1 and the EXAMPLE 2 were “about 6 (about 6 times)”. The lightoutputs of the EXAMPLE 1 and the EXAMPLE 2 became large due to the largeworking amount (depth). It is noted that measurement results measured inthe vertical direction (longitudinal direction) of the n-electrode 50shown in FIG. 2 were the same with those of the lateral direction.

In the semiconductor light emitting device 1 according to theembodiment, the first convex area 80 having a relatively high firstconvex and the second convex area 90 having a relatively low secondconvex are disposed in the light extraction surface, and the secondconvex area 90 is arranged closer to the n-electrode 50. As a result,the peeling-off of the n-electrode 50 in the light extraction surfacecan be reduced. Then, a semiconductor light emitting device which ishighly-reliable and which has a high light output can be provided. Inaddition, according to the semiconductor light emitting device 1 of theembodiment, a semiconductor light emitting device which has a high lightdistribution and a high light output can be provided. Furthermore, sincethe second convex is provided on the light extraction surface inaddition to the first convex, a current dispersion in the semiconductorlayer can be homogenized in comparison with the case where only thefirst convexes are uniformly disposed.

The embodiment of the present invention has been explained. However, thepresent invention is not limited to the embodiment and can be embodiedin various forms without departing from the sprits of the presentinvention. For example, in the first convex area 80 on the lightextraction surface, a base end of the first convex may be formed tobecome closer to the light emitting layer 42 as the first convex leavesthe n-electrode 50. FIG. 9 is a partial cross sectional viewschematically showing the first convex area of a semiconductor lightemitting device which is fabricated as described above. Meanwhile, FIG.9 schematically shows the first convexes observed by (observed by “3DReal Surface View Microscope (VE-9800, manufactured by KEYENCECorporation)”) a scanning electron microscope (SEM). In FIG. 9, it issupposed that the n-electrode 50 (not shown) is arranged on the right.In the example, a top end of each convex has the same height asindicated by a virtual line 901. In addition, in FIG. 9, a crosssectional base end (left side) of the convex at the second from theright and a cross sectional base end (right side) of the convex at thethird from the right are neighbored to each other. The common base endis indicated by a reference number 902. A cross sectional base end(right side) 903 of the convex at the fifth from the right and a baseend 904 of the convex (left side) are located in the same depth. On theother hand, a position of the base end 904 is deeper than that of thebase end 902 by D, assuming that the position of the base end 902 is astandard. Namely, if the convex at the fifth from the right is comparedwith the convex at the second from the right, the convex at the fifthfrom the right is formed to be high from a relatively deep level. Asdescribed above, even in the first convex area, if the convex is formedto become gradually or continuously deeper as the convex leaves theelectrode, the light output can be increased, while reducing thepeeling-off of the electrode.

In addition, in the embodiment, after the upper surface (surface ofn-type semiconductor layer 41) of the semiconductor stack 40 is polishedby CMP, the n-electrode 50 was disposed. However, after the polishingand before forming the n-electrode 50, a convex (first convex) similarto the first convex which will be formed later in the first convex area80 may be formed in advance by processing the electrode formationplanned area. An example of a semiconductor light emitting device whichis fabricated as described above is shown in FIG. 10. A semiconductorlight emitting device 1A whose cross section is shown in FIG. 10 furtherhas the first convex at the interface between the two n-electrodes 50and the semiconductor stack 40. That is, first convex areas 80 a, 80 bare formed just beneath the two n-electrodes 50, respectively.Configuring a semiconductor light emitting device as described above,the adhesiveness between the semiconductor stack 40 and the n-electrodecan be improved, thereby resulting in lowering of the contactresistance.

In addition, the first convex area 80 and the second convex area 90 wereformed by wet-etching using a mask. However, the method for forming thefirst convex area 80 and the second convex area 90 is not limited tothis and dry-etching may also be used. In the dry-etching, the etchingmay be conducted so that the first convex area 80 and the second convexarea 90 are formed step by step by adjusting etching conditions, such asa gas, a vacuum level and a high frequency power in RIE.

In addition, the first convex area 80 and the second convex area 90 maybe formed by a combination of dry-etching and wet etching. An example ofa semiconductor light emitting device fabricated as described above isshown in FIG. 11. With respect to a semiconductor light emitting device1B whose cross section is shown in FIG. 11, first, the first convex area80 is formed using RIE, next, the second convex area 90 is formed usingwet-etching. Here, a cross section of the first convex area 80 may beobserved from two points of view. From a first point of view, we can seethat in FIG. 11, five convexes which are relatively deep and high areformed in the first convex area 80. From a second point of view, we cansee that in FIG. 11, relatively low convexes similar to the convexesformed in the second convex area 90 are formed at a deep level and ashallow level in the first convex area 80. The low convexes can besimultaneously formed in a process for forming the convex in the secondconvex area 90. According to the semiconductor light emitting device 1B,the second convex area 90 is formed adjacent to the n-electrode 50.Then, the peeling-off of the n-electrode 50 on the light emittingsurface can be reduced. In addition, since the relatively deep and highconvexes are formed in the first convex area 80, a light emitting devicehaving a high light output can be provided.

In addition, in the embodiment, a light extraction surface of thesemiconductor stack 40 was formed on the n-type semiconductor layer 41.However, the light extraction surface of the semiconductor stack 40 maybe formed on the p-type semiconductor layer 43, and the first convexarea 80 and the second convex area 90 may be formed on the p-typesemiconductor layer 43. In this case, a p-electrode is formed on thelight extraction surface. Meanwhile, it is preferable to constitute alight emitting device as with the embodiment of the present invention,because the first convex can be deepen in the first convex area 80.

In addition, in the embodiment, the p-electrode 30 was formed on a wholeupper surface of the semiconductor stack 40 in the fabrication process(see FIG. 5B). However, the p-electrode 30 may be partially formed onthe upper surface of the semiconductor stack 40, and a passivation filmidentical to that of the passivation film 60 may be filled in an areawhere the p-electrode 30 is not formed and in the same plane with thep-electrode 30. In this case, it is preferable to form the n-electrode50 and the p-electrode 30 so that the n-electrode 50 and the p-electrode30 are alternately arranged in top view of the semiconductor lightemitting device 1 as seen from the light extraction surface, for furtherincreasing the light extraction efficiency. Meanwhile, the identicalmeans that, for example, if the passivation film 60 is made of SiO₂, thepassivation film filled in the area where the p-electrode 30 is notformed is also SiO₂, and a small change in composition of thepassivation film depending on the formation method may be allowed. Afilling of such a passivation film may be conducted by, for example, ECRsputtering.

In addition, a material consisting of the semiconductor stack 40 of thelight emitting device 1 is not limited to gallium nitride-based compoundsemiconductors. In addition, in the embodiment, the second convex area90 and the first convex area 80 are formed on the light extractionsurface in this order from the n-electrode 50, and the convex in thefirst convex area 80 is formed to be deeper than that in the secondconvex area 90, that is, the convex is deepened with two steps. However,as long as the convex is formed to be higher from a relatively deeplevel as each of the areas leaves the electrode, an equivalent advantagewill be obtained even if the step is more than three.

In addition, in a semiconductor light emitting device, both thep-electrode 30 and the n-electrode 50 may be disposed on the lightextraction surface. In this case, the first convex (or first convex area80) and the second convex (or second convex area 90) may be disposed ona surface of a semiconductor layer on which an electrode (for example,p-electrode 30) to be disposed on the light emitting layer 42 is formed.If the light emitting device is constituted as described above, there isthe advantage to reduce the peeling-off of the electrode disposed on thelight emitting layer 42.

INDUSTRIAL APPLICABILITY

A semiconductor light emitting device according to the present inventioncan be utilized in various fields, for example, lighting, exposure,displays, various kinds of analysis and optical networks.

1. A semiconductor light emitting device, comprising: a semiconductorstack including a light emitting layer between an n-type semiconductorlayer and a p-type semiconductor layer; a substrate on which thesemiconductor stack is mounted; an electrode disposed on a lightextraction surface opposite to a surface that the semiconductor stack ismounted on the substrate; and a plurality of convexes on the lightextraction surface, wherein the plurality of the convexes are disposedin a first convex area and a second convex area; wherein the secondconvex area is located between the first convex area and the electrodeand is adjacent to an interface between the electrode and thesemiconductor stack; wherein a base end of a first convex disposed inthe first convex area is located to be closer to the light emittinglayer than the interface; and wherein a base end of a second convexdisposed in the second convex area is located to be closer to theinterface than the base end of the first convex.
 2. The semiconductorlight emitting device according to claim 1, wherein a height from thebase end to a top end of the first convex is larger than a height fromthe base end to a top end of the second convex.
 3. The semiconductorlight emitting device according to claim 1, wherein the top end of thefirst convex and the top end of the second convex are tapered off to apoint.
 4. The semiconductor light emitting device according to claim 2,wherein the top end of the first convex and the top end of the secondconvex are tapered off to a point.
 5. The semiconductor light emittingdevice according to claim 1, wherein at least the second convex area isdisposed so as to surround the electrode.
 6. The semiconductor lightemitting device according to claim 3, wherein at least the second convexarea is disposed so as to surround the electrode.
 7. The semiconductorlight emitting device according to claim 5, wherein the first convexarea is disposed so as to surround the second convex area and theelectrode.
 8. The semiconductor light emitting device according to claim6, wherein the first convex area is disposed so as to surround thesecond convex area and the electrode.
 9. The semiconductor lightemitting device according to claim 1, wherein the electrodes aredisposed on the light extraction surface apart from each other, and thefirst convex area and the second convex area are disposed in an areabetween the electrodes.
 10. The semiconductor light emitting deviceaccording to claim 3, wherein the electrodes are disposed on the lightextraction surface apart from each other, and the first convex area andthe second convex area are disposed in an area between the electrodes.11. A method for fabricating a semiconductor light emitting device,comprising steps of: forming a semiconductor stack including a lightemitting layer between an n-type semiconductor layer and a p-typesemiconductor layer; forming a resist having an opening surrounding anelectrode formation planned area on a semiconductor layer surface whichforms a light extraction surface opposite to a surface that thesemiconductor stack is mounted on a substrate in such a manner that theopening is narrowed toward a stacking direction of the resist; stackinga mask material on the semiconductor layer surface through the resist;removing the resist on which the mask material is stacked; and etchingthe semiconductor layer surface by masking the electrode formationplanned area.
 12. The method for fabricating a semiconductor lightemitting device according to claim 11, further comprising: using anelectrode material as the mask material.
 13. The semiconductor lightemitting device according to claim 1, wherein the top end of the firstconvex and the top end of the second convex are formed in a non-flatshape.
 14. The semiconductor light emitting device according to claim 3,wherein the top end of the first convex and the top end of the secondconvex are formed in a non-flat shape.
 15. The semiconductor lightemitting device according to claim 1, wherein a base end of the firstconvex is disposed adjacent to a base end of an adjacent first convex,and a base end of the second convex is disposed adjacent to a base endof an adjacent second convex.
 16. The semiconductor light emittingdevice according to claim 3, wherein a base end of the first convex isdisposed adjacent to a base end of an adjacent first convex, and a baseend of the second convex is disposed adjacent to a base end of anadjacent second convex.
 17. The semiconductor light emitting deviceaccording to claim 1, wherein the base end of the first convex in thefirst convex area is formed to be closer to the light emitting layer asthe first convex leaves the electrode.
 18. The semiconductor lightemitting device according to claim 3, wherein the base end of the firstconvex in the first convex area is formed to be closer to the lightemitting layer as the first convex leaves the electrode.
 19. Thesemiconductor light emitting device according to claim 1, wherein athird convex is further disposed in the interface between the electrodeand the semiconductor stack.
 20. The semiconductor light emitting deviceaccording to claim 3, wherein a third convex is further disposed in theinterface between the electrode and the semiconductor stack.